Da Yu

A study of hydrate plug formation in a subsea natural gas pipeline using a novel high-pressure flow loop

The natural gas pipeline from Platform QK18-1 in the southwest of Bohai Bay to the onshore processing facility is a subsea wet gas pipeline exposed to high pressure and low temperature for a long distance. Blockages in the pipeline occur occasionally. To maintain the natural gas flow in the pipeline, we proposed a method for analyzing blockages and ascribed them to the hydrate formation and agglomeration. A new high-pressure flow loop was developed to investigate hydrate plug formation and hydrate particle size, using a mixture of diesel oil, water, and natural gas as experimental fluids. The influences of pressure and initial flow rate were also studied. Experimental results indicated that when the flow rate was below 850 kg/h, gas hydrates would form and then plug the pipeline, even at a low water content (10%) of a water/oil emulsion. Furthermore, some practical suggestions were made for daily management of the subsea pipeline.

Experimental Study on Blockage of Gas Hydrate Slurry in a Flow Loop

Hydrate formation and blockage in long deepwater pipelines has long been a trouble for offshore petroleum production. Consequently, understandings of the procedures as well as influencing factors of hydrate blockage are key points to make reasonable flow assurance strategies. Thus two series of experiments have been conducted in a high-pressure hydrate flow loop newly constructed by multi-phase flow research group in China University of Petroleum (Beijing). One of the systems consists of water and CO2, while the other one includes water, diesel oil and natural gas. The relative time of hydrate blockage has been studied by varying pressure and flow rate for both two systems. The dimensions of hydrate particles in fluid during plugging are also investigated. The results indicate that the influencing factor exerts a similar effect on the relative time for the different systems. Besides, the sizes of particles in the fluid would change significantly due to hydrate formation.Copyright

Experiment Study of Pigging Characteristics in Horizontal Gas-Liquid Flow Pipeline With Different Pig Sizes

During pigging process of long-distance pipeline, pig seals wear due to abrasion on pipe wall, the diameter of seal decreases and even to be smaller than pipe inner diameter as a result. This study has researched the characteristics of pigging processes using pigs different in diameter in horizontal experimental pipe. In the study, mandrel pig with two seals was chosen for experiment. Five pigs different in size were used, and pigging experiments under various flow conditions were carried out in a horizontal air-water flow experimental loop. During experiment, the features of pigging process from pig launcher to trap were observed, the liquid holdup and pressure were detected and collected, pig velocities in different sections of pipe were measured, the velocity of pigging slug front and length of the slug were also measured. The relationship between pig movement and flow conditions was analyzed, the methods to calculate velocity of pigging slug front and length of the slug were obtained and the results calculated were similar to the results measured. Based on the results of experiment, some suggestions were proposed for pigging operation in real pipeline.Copyright